The present invention relates to surgical tools and procedures generally and relates more particularly to the use of ablation to create elongated lesions to treat atrial fibrillation or other medical conditions.
In patients with chronic atrial fibrillation having tachycardia that resistant to medical treatment, the Maze III procedure has been employed. This procedure controls propagation of the depolarization wavefronts in the right and left atria by means of surgical incisions through the walls of the right and left atria. The incisions create blind or dead end conduction pathways, which prevent re-entrant atrial tachycardias from occurring. While the Maze procedure is successful in treating atrial fibrillation, the procedure is quite complex and is currently practiced by only a few very skilled cardiac surgeons in conjunction with other open-heart procedures. The procedure also is quite traumatic to the heart, as in essence the right and left atria are cut into pieces and sewed back together, to define lines of lesion across which the depolarization wavefronts will not propagate.
It has been suggested that procedures similar to the Maze procedure could be instead performed by means of electrosurgical ablation, for example, by applying RF energy to internal or external surfaces of the atria to create lesions across which the depolarization wavefronts will not propagate. Such procedures are disclosed in U.S. Pat. No. 5,895,417, issued to Pomeranz, et al., U.S. Pat. No. 5,575,766, issued to Swartz, et al., U.S. Pat. No. 6,032,077, issued to Pomeranz, U.S. Pat. No. 6,142,944, issued to Swanson, et al. and U.S. Pat. No. 5,871,523, issued to Fleischman, et al, all incorporated herein by reference in their entireties. Hemostat type electrosurgical or cryo-ablation devices for use in performing such procedures are described in U.S. Pat. No. 5,733,280 issued to Avitall, U.S. Pat. No. 6,237,605 issued to Vaska, et al, U.S. Pat. No. 6,161,543, issued to Cox, et al., PCT published Application No. WO99/59486, by Wang and in pending U.S. patent application Ser. No. 09/747,609 filed Dec. 22, 2000 by Hooven, et al., all incorporated herein by reference in their entireties. In order for such procedures to be effective it is desirable that the electrosurgically created lesions are continuous along their length and extend completely through the tissue of the heart. In order for such procedures to be effective it is desirable that the electrosurgically created lesions are continuous along their length and extend completely through the tissue of the heart.
According to a preferred embodiment of the present invention, a maze type procedure may be performed using one or more bipolar electrosurgical hemostats, which apply ablation energy (e.g. RF energy) across the walls of the left and right atria by means of delivery means (e.g. electrodes) located on either side of the atrial walls. In a preferred embodiment of the invention, the hemostats are provided with elongated R-F electrodes capable of assuming various straight and curved configurations. In the particular embodiment of the invention described herein, a bipolar electrosurgical hemostat is provided, shapeable, for example, to a set of configurations adapted to allow the physician to approximate the incisions that would occur during the Maze III procedure as described in the book xe2x80x98Cardiac Surgery Operative Techniquexe2x80x99 by Donald B. Doty, M.D. at pages 410-419, incorporated herein by reference in its entirety, and herafter referred to as the xe2x80x9cDoty referencexe2x80x9d. Other curved configurations may also be accomplished, using the shapeable hemostat of the present invention, to allow approximation of the incisions that would be provided by other forms of the Maze procedure or to perform other ablation procedures.
The shapeable hemostat according to a preferred embodiment of the present invention is provided with elongated jaws that carry electrodes or other means for applying ablation energy to a patent""s heart. The jaws of the hemostat may each carry a single, elongated electrode or may each carry a series of electrodes. While the preferred embodiment of the invention as disclosed takes the form of a hemostat with R-F electrodes extending along both jaws, it is believed the invention may also usefully be practiced in a device having only a single elongated shapeable electrode or series of electrodes, for application of ablation energy to only the inner or outer surface of the wall of a heart chamber.
The jaws are fabricated of or provided with a core formed of a shape memory material, e.g. a nickel titanium alloy such as Nitinol, a copper-nicel aluminum or copper zinc aluminum alloy (SME brass) or a plastic having shape memory properties. If the shape memory material is not itself biocompatble, it should be encased in a biocompatible covering, e.g. encapsulated within the material of the jaws. The material chosen preferably displays its memorized configuration at a temperature above the temperature to which it will be heated during the ablation procedure. This temperature will be dependant on the construction of the jaws of the hemostat, and will vary depending on the degree of thermal insulation between the electrode and the shape memory material. If the electrode itself is the shape memory component, then the transition temperature should be above 50 degrees Celsius. In any case, the transition temperature should be well above body temperature. The transition temperature should be below the temperature to which it will be heated to resume its memorized configuration, e.g. less than 100 degrees Celsius, if heated using boiling water, above 100 degrees Celsius if placed in a heater. The specific composition of the alloy or plastic material can be chosen to control transition temperature, using standard techniques. The jaws of the hemostat may thereby be shaped at room temperature and will retain their shape during subsequent use in the body to ablate tissue. The memorized configuration may be straight or curved.
In use, the jaws of the hemostat are shaped manually or with the use of a bending fixture to exhibit a desired configuration for use in producing a particular lesion. As noted above, these lesions may be produced as part of a procedure corresponding to a Maze type procedure. After the lesion is produced, the shape memory material in the jaws of the hemostat is heated to a temperature above its transition temperature so that the jaws return to their memorized configuration and may then either be used in this configuration to produce the next lesion or may be again shaped to an alternative desired configuration. This process is continued until all desired lesions have been produced. Because the jaws are returned to their memorized configuration, e.g. straight, before reshaping, any kinks or curves resulting from the previous reshaping will be eliminated. This allows the jaws to be successively reshaped, with subsequent reshapings unaffected by previous reshapings.
The jaws may be heated by any convenient means, for example by placement in hot water, placement in or on an electric heater, or by means of resistive heaters built into the jaws themselves. The configurations assumable by the hemostat jaws may be straight, curved or bent, adapted to an individual patient according to the judgment of the physician. Alternatively, the physician may be provided with a set of bending fixtures to provide a pre-determined set of curved configurations, each configuration associated with one or more of a predetermined set of desired lesions.
The particular embodiment of the invention as disclosed herein is described in the context of hemostats particularly adapted for treatment of atrial fibrillation during open chest surgery, with the patient undergoing cardiopulmonary bypass. However, the present invention is also believed applicable to closed chest procedures, in which the heart is observed thoracoscopically and access is provided by means of thoracoscopic surgical ports. It is believed the invention is also applicable to other procedures involving creation of a set of elongated lesions in heart tissue or elsewhere in the body.